1. Field of the Invention
This invention relates to an image recording method and apparatus for recording a stereographic image on a holographic stereogram and an image reproducing method and apparatus for reproducing a stereographic image from the holographic stereogram.
2. Description of the Related Art
A holographic stereogram is produced by sequentially recording a large number of images, obtained on sequentially shooting an object from different viewing points, as original images, as strip- or dot-shaped hologram elements, on a sole recording medium.
For example, in a holographic stereogram having the parallax information only in the transverse direction, plural original images 301a to 301e, obtained on sequentially imaging an object 300 from plural viewing points in the transverse direction, are sequentially exposed to light and recorded on a recording medium for hologram 302 as strip-shaped hologram elements.
With the present holographic stereogram, since the picture information obtained on sequentially imaging an object from plural viewing points in the horizontal direction is sequentially recorded in the transverse direction as strip-shaped hologram elements, the two-dimensional pictures as viewed by left and right eyes of a viewer if the holographic stereogram is viewed by the viewer with both eyes. This the observer feels the parallax so that a three-dimensional image is reproduced.
However, with the conventional holographic stereogram, an optimum reproduced picture cannot be produced. Specifically, with the conventional holographic stereogram, a reproduced image is unclear, dark and poor in contrast, while the reproduced image has a narrow angle of visibility.
For enabling an optimum picture to be produced from a holographic stereogram, it is necessary to completely fix a recording medium for hologram during light exposure of the recoding image to prevent minute vibrations even of the order of the light wavelength. During production of the holographic stereogram, the recording medium for hologram is moved little by little for sequentially recording an extremely large number of hologram elements. For providing a practically useful picture recording device used for producing a holographic stereogram, the recording medium for hologram needs to be transferred quickly during fabrication of the holographic stereogram. Therefore, means for holding and transferring the recording medium for hologram needs to be such a device in which not only the recording medium for hologram can be transferred quickly, but also no vibrations of the recording medium for hologram are allowed after completion and halting of the recording medium for hologram.
For example, if the recording medium for hologram is transferred using an ordinary electrically driven sliding stage, the time of the order of 2 seconds is required until the vibrations of the recording medium for hologram are attenuated, after transfer of the recording medium for hologram, to the extent that the hologram elements can be formed. Therefore, if the recording medium for hologram is transferred each time the hologram element is formed using the electrically driven stage, an extremely long time is consumed until completion of a sole holographic stereogram.
The present inventors have conducted searches into holding and transfer means capable of suppressing the vibrations of the recording medium for hologram more quickly. Thus it has been found that, by loading an elongated recording medium for hologram between two parallel rolls, holding the recording medium for hologram by a torsion coil spring for producing a pre-set tensile force and by causing an object light to fall on the recording medium for hologram placed between the two parallel rolls, the vibrations of the recording medium for hologram can be suppressed more promptly. By employing this method, the time until attenuation of the vibrations after transfer of the recording medium for hologram has been reduced to less than one fourth that when the electrically driven sliding stage is used. However, if this method is employed, the vibrations cannot be suppressed completely. Thus, it has been desired to develop a method and apparatus capable of further suppressing vibrations of the recording medium for hologram.
In a usual hologram, an illuminating light source for reproducing a three-dimensional picture and a hologram are spatially separated from each other. Thus, in a usual hologram, a broad spacing is required for reproduction. On the other hand, for reproduction under an optimum condition, the relative positions of the hologram and the illuminating light source need to be set under a pre-set condition. This applies for a holographic stereogram made up of plural hologram elements.
If the illuminating light source and the hologram are unified with each other, the spacing for illumination becomes unnecessary to make it possible to reduce the size of the apparatus. Moreover, since the relative positions of the hologram and the illuminating light become always constant, reproduction can be performed at all times under optimum conditions. As a hologram for realizing this, there is known an edge-lit system hologram in which recording and/or reproduction is carried out with a recording medium bonded to a transparent light-inlet block.
With such edge-lit system hologram, the optical system for reproduction can be reduced in size and reproduction can be performed at all times under optimum conditions by unifying the light source for the reproducing illuminating light and a light inlet block. Also, since the angle of incidence of the reproducing illuminating light is increased with the edge-lit type hologram, an image is not reproduced by the light incident from outside the light inlet block. Thus the edge lit type hologram is in use in a field in which it is not desirable for an image to be reproduced with, for example, the sunlight, such as in a head-up display device.
For producing a transmission type hologram in which a three-dimensional image is reproduced by the light transmitted through the recording medium, a recording medium for hologram 311 is bonded to a surface 310a of a light inlet block 310 formed of a glass plate or a synthetic resin plate of a suitable thickness, as shown in FIG. 2. At this time, the recording medium for hologram 311 is bonded via an index matching liquid 312 to the light inlet block 310. An object light beam 314 from an object 313 is illuminated from an other surface 310b of the light inlet block 310 towards the recording medium for hologram 311, while a reference light beam 315 is illuminated from an end face 310c of the light inlet block 310 towards the recording medium for hologram 311. This completes a transmission type edge-lit hologram.
For reproducing the thus produced transmission type edge-lit hologram, the hologram 321 is bonded on an end face 320a of the light inlet block 320 via an index matching liquid 322 and a reproducing illuminating light beam 323 is illuminated from the end face 320b of the light inlet block 320 towards the hologram 321. The light transmitted through the hologram 321 is diffracted at this time by the hologram 321. A reproduced image 325 is generated by a diffracted light beam 324 so as to be viewed by a viewer 326.
For producing a reflection type hologram in which a three-dimensional image is reproduced by the light reflected by the recording medium, by the edge-lit system, a recording medium 332 is bonded via an index matching liquid 331 on one surface 330a of a light inlet block 330, as in the case of producing a transmission type edge-lit hologram, as shown in FIG. 4. For the reflection type hologram, an object light beam 334 from an object 333 is illuminated from the side of bonding the recording medium 332 towards the recording medium 332, while a reference light beam 335 is illuminated from an end face 330b of the light inlet block 330. This completes the edge-lit reflection type hologram.
For reproducing the edge-lit reflection type hologram, thus produced, usually a hologram 341 is bonded via an index matching liquid 342 to a surface 340a of a light inlet block 340, as shown in FIG. 5, and a reproducing illuminating light beam 343 is illuminated towards the hologram 341 from an end face 340b of the light inlet block 340. The light reflected at this time by the hologram 341 is diffracted by the hologram 341. A reproduced image is generated by this diffracted light 344 so as to be viewed by a viewer 346.
If such edge-lit system is applied to a holographic stereogram, and an image is generated as if there were an object behind the light inlet block, the reproduced image is difficult to view and lowered in stereographic feeling to detract from the display effect. It is therefore desirable that an image can be reproduced so that an object will be as close to the view as possible. However, with the edge-lit system holographic stereogram, an image is reproduced as if the object as viewed by the viewer were at back of the light inlet block, as shown in FIG. 5.
For producing the image as though the object were as close to the viewer as possible, a transmission type edge-lit system holographic stereogram is preferably employed. However, if the stereogram is recorded by the transmission type hologram, both the object light beam and the reference light beam need to be incident on one side of the recording medium for hologram. This lowers the degree of freedom in arranging the optical system to raise difficulties in constituting an optimum optical system.
Moreover, if desired to assure a broad angle of visibility angle in the up-and-down direction in reproducing a holographic stereogram, a one-dimensional diffusion plate for diffusing the object light beam in a one-dimensional in-plane direction is desirably provided in the vicinity of the recording medium for hologram on the object light beam incident side. However, with the transmission type recording in which a light incident block needs to be arranged towards the object light beam incident side, it becomes impossible to array this one-dimensional diffusion plate. Consequently, it has hitherto not been practiced to produce the edge-lit system holographic stereogram as a transmission type stereogram.